(a) Field of the Invention
The present invention is related to a contact type electret condenser pickup, and more particularly, to one that contacts human skin to pick up micro vibration generated during talking to realize electro-acoustic transduction.
(b) Description of the Prior Art
How to maintain clear and effective communications in a highly noisy environment, e.g., fire fighting site or a battlefield has been a problem desperately to be solved. Currently, a contact type vibration pickup is usually used for electro-acoustic transducer essentially based on electromagnetic and piezoelectric working principle. Both types of the transducers however have been found with certain problems in their talking clarity, output sensitivity, and anti noise performance.
A condenser pickup of the prior art has a thinner metal diaphragm serving as a plate (a vibration part) of a condenser and a fixed thicker metal plate facing the diaphragm as a fixed plate of capacitance (back plate); an air medium existing between the vibration part and the back plate functions as a condenser; and an elastic structure of the thinner metal diaphragm is capable of picking up vibration of external acoustic wave to create minor axial displacement thus to change an air gap between the vibration part and the back plate resulting in changed capacity of electric charge of the condenser comprised of both plates. Changed electric charge resulted from changed acoustic pressure further change in output voltage, thus to avail a current in specific size and direction. A condenser pickup provides advantage of good frequency response, low noise level, and low distortion; and disadvantages of comparatively complicated output interface circuit, lower level of output signals, being vulnerable to interference by external stray signals, and preventing from forming a complete set with associate apparatus.